This invention is generally directed to processes for the preparation of phthalocyanines, and more specifically to processes for the preparation of x-metal free phthalocyanine. In one embodiment, the present invention relates to a simple, economical process for the preparation of x-metal free phthalocyanine photogenerating components by, for example, a pigment grinding method inclusive of attrition and subsequent washing. In accordance with an embodiment of the present invention, the process thereof comprises the polymorphic conversion of alpha-metal free phthalocyanine (.alpha.-H.sub.2 Pc) to x-metal free phthalocyanine (x-H.sub.2 Pc) by a pigment grinding method whereby the resulting phthalocyanine, which is obtained in a high purity of, for example, equal to or greater than 97 percent, can be selected as a photogenerating pigment, especially as an infrared photogenerating pigment in layered photoresponsive imaging members, which members are comprised of charge or hole transport layers comprised of, for example, aryl amines as illustrated in U.S. Pat. No. 4,265,990 and copending application U.S. Ser. No. 215,099, the disclosures of which are totally incorporated herein by reference. The aforementioned photoresponsive or photoconductive imaging members can be selected for various electrophotographic imaging and printing processes, especially xerographic processes wherein, for example, latent images are formed thereon followed by development and transfer to a suitable substrate.
Processes for the preparation of x-metal free phthalocyanine are known. However, these processes are in most instances time consuming, or not effectively and commercially scalable, and the electrical characteristics of the x-metal free phthalocyanine formulated with such processes may be undesirable or inferior than what is needed for photogenerating pigments. In U.S. Pat. No. 3,357,989, the disclosure of which is totally incorporated herein by reference, there is described a milling process for converting alpha-metal free phthalocyanine to x-metal free phthalocyanine by prolonged grinding of the dry alpha-form material. The aforementioned process is not considered suitable for large scale manufacturing purpose since, for example, this process would require extensive time periods, that is several weeks, and correspondingly high consumption of energy for completing the conversion in addition to a reproducibility problem encountered because of the inhomogeneous nature of grinding dry material. More specifically, in the '989 patent it is indicated that a metal free phthalocyanine may be converted to the x form by heat milling or salt milling alpha phthalocyanine for a sufficient time, reference for example column 3, beginning at around line 18, and the working Examples, columns 3 and 4. In column 4, beginning at line 50, it is indicated that any grinding process may be used to convert the alpha or beta metal free phthalocynine to the x polymorph, processes including ball milling with ceramic or metallic balls, salt milling and the use of spex mixer mill which is not believed to be attritor but rather is a shaker containing one steel ball and is primarily used by dentists for mixing purposes; and washing with water, see Example 1. Another method for the preparation of x-metal free phthalocyanine is illustrated in U.S. Pat. No. 3,594,163, the disclosure of which is totally incorporated herein by reference, which comprises mixing alpha-metal free phthalocyanine with a portion of x-metal free phthalocyanine in an aliphatic organic solvent and maintaining the mixing until alpha-metal free phthalocyanine is converted to the corresponding x-form material. The x-metal free phthalocyanine produced by this method, however, has some disadvantages in that, for example, the xerographic properties thereof, such as lower photoactivity, render the material less useful as a photoconductor component in electrophotographic applications. Also, in U.S. Pat. No. 3,932,182 there is described the conversion of alpha-metal free phthalocyanine to the x-form by heating ultra thin evaporated films, about 1,400 Angstroms thick, of alpha form to 450.degree. C. Disadvantages resulting with the aforementioned process reside in the generation of small amounts of x-metal free phthalocyanine on large surface areas about, that is for example 0.25 gram of x-metal phthalocyanine can be prepared on the surface of one square centimeter, the process is not cost effective for producing large quantities of x-metal free phthalocyanine as it would involve expensive vacuum evaporator, high heating cost and lengthy process times. The aforementioned disadvantages are avoided, or minimized with the processes of the present invention wherein, for example, large quantities, that is for example 10 pounds or more of x-metal free phthalocyanine with excellent xerographic properties, such as low dark decay, high photosensitivity and stable cycling, can be obtained can be obtained for electrophotographic processes.
In a patentability search report, in addition to the U.S. Pat. No. 3,357,989 patent mentioned herein there were located as references illustrative of the prior art U.S. Pat. Nos. 3,492,309; 3,816,118; 4,426,434 and 4,443,528. Additionally, in U.S. Pat. No. 4,814,441, the disclosure of which is totally incorporated herein by reference, there is illustrated a novel x-phthalocyanine with specific characteristics which is obtained by preparing alpha phthalocyanine by intensive dry milling into a mixture which consists of the alpha phthalocyanine in the x modification with the content of the x-phthalocyanine being from about 40 to about 75 percent by weight based on the weight of the mixture, which mixture is then heat treated with a solvent, see column 1, beginning at line 25, and continuing on to column 2. As is indicated in column 1 of the '441 patent, beginning at line 45, the dry milling process is advantageously carried out in the mill, for example a ball mill, rotary mill and the like, and that alcohols and particularly alkanols such as methanol, propanol are suitable for the solvent treatment, see column 1, beginning at line 50. It is also indicated in column 1, beginning at line 65, that in order to suppress the formation of beta phthalocyanine it has been proven advantageous in some cases to carry out the treatment with the inert organic solvent also in the presence of water, the amount of water being from 20 to 60 percent by weight based on the liquid system. The resulting x-phthalocyanines have advantages in the coatings sector, see column 4, beginning at line 45, and further the pigments may be used for printing inks, reference column 4, beginning at line 50.
In U.S. Pat. No. 4,508,803, the disclosure of which is totally incorporated herein by reference, there is described an improved photoresponsive device comprised of a supporting substrate, a hole blocking layer, an optional adhesive interface layer, an inorganic photogenerating layer, a photoconducting composition layer comprised of benzyl fluorinated squaraine compositions, and a hole transport layer. Other representative patents disclosing photoconductive devices with squaraine components therein include U.S. Pat. Nos. 4,507,408; 4,552,822; 4,559,286; 4,507,480; 4,524,220; 4,524,219; 4,524,218; 4,525,592; 4,559,286; 4,415,639; 4,471,041 and 4,486,520. The disclosures of each of the aforementioned patents are totally incorporated herein by reference.
The x-metal free phthalocyanines obtained with the process of the present invention can be selected as a photogenerating pigment in the above-mentioned layered photoresponsive imaging members, and other similar imaging members.